U.S. patent application number 15/616077 was filed with the patent office on 2018-01-04 for gas concentration measurement apparatus.
This patent application is currently assigned to HORIBA, LTD.. The applicant listed for this patent is HORIBA, LTD.. Invention is credited to Kimihiko ARIMOTO, Yasuo FURUKAWA, Daisuke KITAKI, Tomoko SEKO, Yutaro TSUCHISAKA, Issei YOKOYAMA.
Application Number | 20180003626 15/616077 |
Document ID | / |
Family ID | 60806487 |
Filed Date | 2018-01-04 |
United States Patent
Application |
20180003626 |
Kind Code |
A1 |
ARIMOTO; Kimihiko ; et
al. |
January 4, 2018 |
GAS CONCENTRATION MEASUREMENT APPARATUS
Abstract
In order to provide a gas concentration measurement apparatus
that suppresses any change in the temperature of an optical fiber,
and also makes it difficult for any effects to appear in the
measurement accuracy due to air from the surrounding environment
penetrating the optical path of the measurement light while using
only a simple structure and without causing any excessive energy
consumption there are provided a first sealing component provided
between an incident surface of a gas cell and a first end surface
that is formed at a periphery of an emission aperture of a
light-emitting unit so as to enclose the periphery of the emission
aperture, and a second sealing component provided between an
emission surface of the gas cell and a second end surface that is
formed at a periphery of an incident aperture of a light-receiving
unit so as to enclose the periphery of the incident aperture.
Inventors: |
ARIMOTO; Kimihiko; (Kyoto,
JP) ; YOKOYAMA; Issei; (Kyoto, JP) ; SEKO;
Tomoko; (Kyoto, JP) ; TSUCHISAKA; Yutaro;
(Kyoto, JP) ; KITAKI; Daisuke; (Kyoto, JP)
; FURUKAWA; Yasuo; (Kyoto, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HORIBA, LTD. |
Kyoto-shi |
|
JP |
|
|
Assignee: |
HORIBA, LTD.
Kyoto-shi
JP
|
Family ID: |
60806487 |
Appl. No.: |
15/616077 |
Filed: |
June 7, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 21/0332 20130101;
G01N 21/359 20130101; G01N 2291/0212 20130101; G01N 21/3504
20130101 |
International
Class: |
G01N 21/3504 20140101
G01N021/3504 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2016 |
JP |
2016-130749 |
Jun 30, 2016 |
JP |
2016-130750 |
Claims
1. A gas concentration measurement apparatus comprising: a gas cell
equipped with an incident surface through which measurement light
is irradiated into an interior of the gas cell, and an emission
surface through which the measurement light is emitted to the
outside of the gas cell, and that is formed such that a sample gas
is introduced into the interior of the gas cell; a heater mechanism
that heats the gas cell; a light-emitting unit that causes
measurement light that has been emitted from an end surface of a
first optical fiber provided inside the light-emitting unit to be
emitted into the gas cell via an emission aperture; a
light-receiving unit that causes measurement light that has passed
through the gas cell and is to be irradiated into an incident
aperture to be irradiated onto an end surface of a second optical
fiber provided inside the light-receiving unit; a first sealing
component that is provided between the incident surface of the gas
cell and a first end surface that is formed at a periphery of the
emission aperture of the light-emitting unit so as to enclose the
periphery of the emission aperture; and a second sealing component
that is provided between the emission surface of the gas cell and a
second end surface that is formed at a periphery of the incident
aperture of the light-receiving unit so as to enclose the periphery
of the incident aperture.
2. The gas concentration measurement apparatus according to claim
1, wherein the first sealing component and the second sealing
component are O-rings.
3. The gas concentration measurement apparatus according to claim
1, wherein, in a state in which the first sealing component and the
second sealing component have been provided, a first gap is formed
between the incident surface of the gas cell and the first end
surface of the light-emitting unit, and a second gap is formed
between the emission surface of the gas cell and the second end
surface of the light-receiving unit.
4. The gas concentration measurement apparatus according to claim
3, wherein the first gap and the second gap have substantially the
same size, and a thickness dimension prior to deformation of each
of the first sealing component and the second sealing component is
set so as to be larger than the first gap and the second gap.
5. The gas concentration measurement apparatus according to claim
1, wherein the gas cell is formed from quartz glass, and wherein
the light-emitting unit is provided with: a first optical fiber via
whose end surface measurement light is emitted; a first lens that
performs collimation on the measurement light emitted from the end
surface of the first optical fiber; and a first holder that is made
from resin and inside which are held the first optical fiber and
the first lens, with an emission aperture and the first end surface
being formed in the first holder, and wherein the light-receiving
unit is provided with: a second optical fiber via whose end surface
measurement light is introduced; a second lens that condenses
measurement light onto the end surface of the second optical fiber;
and a second holder that is made from resin and inside which are
held the second optical fiber and the second lens, with an incident
aperture and the second end surface being formed in the second
holder.
6. The gas concentration measurement apparatus according to claim
1, wherein the heater mechanism is a jacket heater that is wrapped
around the periphery of the gas cell, and is provided so as to be
separated from the first end surface and the second end
surface.
7. The gas concentration measurement apparatus according to claim
1, wherein there are further provided: a fixing mechanism that
fixes the first end surface of the light-emitting unit and the
second end surface of the light-receiving unit such that these are
a predetermined distance apart from each other; and a temporary
holding mechanism that temporarily holds the gas cell such that the
gas cell is able to slide in the direction of the optical axis of
the measurement light, and a structure is employed in which the gas
cell is gripped between the light-emitting unit and the
light-receiving unit by being pressed by repulsive force from the
first sealing component and the second sealing component.
8. The gas concentration measurement apparatus according to claim
1, wherein the sample gas introduced into the gas cell contains
H.sub.2O.sub.2, and the measurement light contains light in a near
infrared region, and there is further provided a concentration
calculator that calculates a concentration of the H.sub.2O.sub.2
gas introduced into the gas cell interior based on an absorbance of
the measurement light received by the light-receiving unit.
9. A gas concentration measurement apparatus comprising: a gas cell
equipped with a cell main body into whose interior sample gas is
introduced, an incident portion through which measurement light is
irradiated into an interior of the cell main body, and an emission
portion through which the measurement light that has passed through
the cell main body is emitted to the outside; a heater mechanism
that heats the gas cell, or the sample gas introduced into the gas
cell; a first optical fiber that is provided so as to emit
measurement light from an end surface thereof, and cause this
measurement light to be irradiated into the incident portion; and a
second optical fiber that is provided such that the measurement
light that has passed through the emission portion is irradiated
onto an end surface of the second optical fiber, wherein the
incident portion and the emission portion have a double-glazed
window structure whose interior is either maintained in a vacuum,
or holds a gas.
10. The gas concentration measurement apparatus according to claim
9, wherein the double-glazed window structure comprises: an inner
window plate that is attached to the cell main body; an outer
window plate that is provided at a predetermined distance from the
inner window plate so as to be parallel with the inner window
plate; and an enclosing wall that connects the inner window plate
to the outer window plate so as to form a closed space, wherein an
interior of the closed space is either maintained in a vacuum, or
holds a gas.
11. The gas concentration measurement apparatus according to claim
9, wherein the cell main body has an elongated shape, and the
incident portion and the emission portion are each joined to a
mutually different end portion of the cell main body, and there is
further provided a supporting mechanism that supports one point of
a central portion of the cell main body.
12. The gas concentration measurement apparatus according to claim
9, wherein the cell main body has an elongated shape, and the
incident portion and the emission portion are each joined to a
mutually different end portion of the cell main body, and there are
further provided supporting mechanisms that support both ends of
the gas cell at the incident portion and the emission portion.
13. The gas concentration measurement apparatus according to claim
9, wherein the heater mechanism is a jacket heater that is wrapped
around the cell main body.
14. The gas concentration measurement apparatus according to claim
9, wherein the gas cell is formed from a plurality of quartz glass
pieces, and the incident portion and the emission portion are
bonded via optical contact bonding to the cell main body.
15. The gas concentration measurement apparatus according to claim
9, wherein there are further provided: a light-emitting unit that
causes measurement light that has been emitted from an end surface
of the first optical fiber provided inside the light-emitting unit
to be emitted into the gas cell via an emission aperture; a
light-receiving unit that causes measurement light that has passed
through the gas cell and is to be irradiated into an incident
aperture to be irradiated onto an end surface of a second optical
fiber provided inside the light-receiving unit; a first sealing
component that is provided between an incident surface, which is a
surface on the incident portion that measurement light first
strikes from an outer side, and a first end surface that is formed
at a periphery of the emission aperture of the light-emitting unit,
so as to enclose the periphery of the emission aperture; and a
second sealing component that is provided between an emission
surface, which is a surface on the emission portion that
measurement light is ultimately emitted from, and a second end
surface that is formed at a periphery of the incident aperture of
the light-receiving unit, so as to enclose the periphery of the
incident aperture.
16. The gas concentration measurement apparatus according to claim
9, wherein the sample gas introduced into the gas cell contains
H.sub.2O.sub.2, and the measurement light contains light in a near
infrared region, and there is further provided a concentration
calculator that calculates a concentration of the H.sub.2O.sub.2
gas introduced into the gas cell interior based on an absorbance of
the measurement light received by the light-receiving unit.
Description
TECHNICAL FIELD
[0001] The present invention relates to a gas concentration
measurement apparatus that introduces gas into a gas cell and also
measures the concentration of this gas based on the absorptivity
thereof.
TECHNICAL BACKGROUND
[0002] For example, in a semiconductor manufacturing process,
various liquid materials are gasified by being heated so as to form
material gases, and these material gases are then introduced into a
vacuum chamber where film formation on substrates is performed. In
order to maintain the quality of the semiconductors being
manufactured, it is necessary for the concentrations of the
introduced material gases to be kept constant.
[0003] In order to perform this type of concentration control, a
gas concentration measurement apparatus that measures the
concentration of material gases based on an NIR method (i.e., on
near infrared spectroscopy) is incorporated into the process.
[0004] One gas concentration measurement apparatus of this type
(see Patent document 1) is a gas concentration measurement
apparatus that is provided with a gas cell into which a material
gas is introduced, a first optical fiber into one end of which
measurement light emitted from a halogen light source is introduced
and from another end of which the measurement light is emitted, a
first lens that performs collimation on the measurement light
emitted from the first optical fiber and then emits the measurement
light into the gas cell, a second lens that condenses the
measurement light that has been transmitted through the interior of
the gas cell, and a second optical fiber into one end of which the
measurement light condensed by the second lens is introduced and
from another end of which the measurement light is emitted into a
photodetector. The gas concentration is then calculated from the
absorbance of light of a predetermined wavelength measured by the
photodetector, and a calibration curve that has been prepared in
advance and shows a relationship between the concentration and the
absorbance for various types of gases.
[0005] In order to prevent a material gas cooling inside the gas
cell and becoming reliquefied, and consequently affecting the
concentration measurement, it is necessary to heat the gas cell
itself. However, the temperature changes generated by this heat
also cause the light-guiding characteristics of the respective
optical fibers provided adjacent to the gas cell to change, and the
effects of this appear in the measured absorbance. In some cases,
this causes the accuracy of the concentration measurement to
deteriorate.
[0006] In order to solve this type of problem, consideration might
be given to providing a gap so as to separate the holders
respectively holding each optical fiber and each lens from the gas
cell, so as to make if difficult for the heat used to heat the gas
cell to be conducted via the respective holders to the respective
optical fibers.
[0007] However, if gaps are provided between the respective holders
and the gas cell, then there is a possibility that air from the
surrounding environment will flow in through these gaps and
penetrate the optical path of the measurement light so that the
absorbance of the measurement light will be affected by gases other
than the material gas. Moreover, when the gas cell is heated by a
heater mechanism so that reliquefaction of a sample gas is
prevented, then because the temperature of the lens is lower than
that of the surrounding air which has been heated by the heater
mechanism, condensation ends up being formed on the lens and this
changes the characteristics of the optical system. Having said
that, if the entire gas concentration measurement apparatus is
covered by a case in an attempt to keep the temperature of the air
in the surrounding environment constant, then mutually opposing
forms of control, namely, control to heat the gas cell and control
to cool the respective holders need to be performed simultaneously.
As a result, energy is wasted in the system as a whole.
DOCUMENTS OF THE PRIOR ART
Patent Documents
[0008] [Patent document 1] Japanese Unexamined Patent Application
(JP-A) Laid-Open No. H6-94609
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0009] The present invention was therefore conceived with the
intention of solving all of the above-described problems, and it is
an object thereof to provide a gas concentration measurement
apparatus that suppresses any change in the temperature of an
optical fiber, and also makes it difficult for any effects to
appear in the measurement accuracy due to air from the surrounding
environment penetrating the optical path of the measurement light
while using only a simple structure and without causing any
excessive energy consumption.
[0010] The present invention was conceived in view of the
above-described problems and it is a further object thereof to
provide a gas concentration measurement apparatus that is able to
prevent reliquefaction by maintaining a sample gas inside a gas
cell at a high temperature, and makes it difficult for heat to be
conducted to an optical fiber that is used to emit or receive
measurement light, and that, as a consequence, suppresses any
change in the light-guiding characteristics of the gas
concentration measurement apparatus.
Means for Solving the Problem
[0011] Namely, a gas concentration measurement apparatus according
to the present invention is provided with a gas cell equipped with
an incident surface through which measurement light is irradiated
into an interior of the gas cell, and an emission surface through
which the measurement light is emitted to the outside of the gas
cell, and that is formed such that a sample gas is introduced into
the interior of the gas cell, a heater mechanism that heats the gas
cell, a light-emitting unit that causes measurement light that has
been emitted from an end surface of a first optical fiber provided
inside the light-emitting unit to be emitted into the gas cell via
an emission aperture, a light-receiving unit that causes
measurement light that has passed through the gas cell and is to be
irradiated into an incident aperture to be irradiated onto an end
surface of a second optical fiber provided inside the
light-receiving unit, a first sealing component that is provided
between the incident surface of the gas cell and a first end
surface that is formed at a periphery of the emission aperture of
the light-emitting unit so as to enclose the periphery of the
emission aperture, and a second sealing component that is provided
between the emission surface of the gas cell and a second end
surface that is formed at a periphery of the incident aperture of
the light-receiving unit so as to enclose the periphery of the
incident aperture.
[0012] If this type of structure is employed, then because the
light-emitting unit and the light-receiving unit are not formed
integrally with the gas cell, but are separated therefrom, even if
the gas cell is heated by the heater mechanism in order to prevent
reliquification of the sample gas, it becomes difficult for this
heat to be conducted to the first optical fiber and the second
optical fiber. Accordingly, it is also difficult for temperature
changes to occur in the first optical fiber and the second optical
fiber, and the light-guiding characteristics thereof can be kept
substantially constant.
[0013] Furthermore, air from the surrounding environment or other
gases are prevented from penetrating the emission aperture or the
incident aperture by the first sealing component and the second
sealing component. Accordingly, it is possible to prevent errors in
the measured absorbance that are caused by gases other than the
sample gas circulating on the optical path of the measurement light
from occurring. Furthermore, because there is no penetration by air
and the like from the surrounding environment that has been warmed
by the heater mechanism, air and the like from the surrounding
environment does not become condensed on low-temperature components
forming the light-emitting unit and the light-receiving unit and
consequently cause moisture to form, so that any changes in the
optical system can be prevented from occurring.
[0014] Because of these advantages, it is possible to maintain a
high level of accuracy when measuring gas concentrations while
using only a simple structure and without causing any excessive
energy consumption.
[0015] In order to reduce the conduction of heat from the gas cell
to the light-emitting unit and the light-receiving unit via the
first sealing component and the second sealing component, and to
thereby make it possible to further prevent any change in the
temperature of the first optical fiber and the second optical
fiber, and maintain a high level of accuracy when measuring gas
concentrations, it is also possible for the first sealing component
and the second sealing component to be formed by O-rings. These
O-rings may be formed, for example, from resin, or they may be
formed from metal.
[0016] In order to ensure that the light-emitting unit and the
light-receiving unit do not come into direct contact with the gas
cell, and in order to substantially limit the heat conduction path
from the gas cell to being a path that goes via the first sealing
component and the second sealing component so that there are no
changes in the temperature of the first optical fiber and the
second optical fiber, it is desirable that, in a state in which the
first sealing component and the second sealing component have been
provided, a first gap be formed between the incident surface of the
gas cell and the first end surface of the light-emitting unit, and
a second gap be formed between the emission surface of the gas cell
and the second end surface of the light-receiving unit.
[0017] In order to ensure that the first sealing component and the
second sealing component are compressed so that air and the like
from the surrounding environment can be reliably prevented from
penetrating the emission aperture and the incident aperture, at the
same time as heat conduction from the gas cell to the
light-emitting unit and the light receiving unit is prevented, it
is also possible for the first gap and the second gap to be
substantially the same size, and for a thickness dimension prior to
deformation of each of the first sealing component and the second
sealing component to be set so as to be larger than the first gap
and the second gap.
[0018] Even if the sample gas is, for example, a gas that is highly
reactive with metal such as H.sub.2O.sub.2, in order to suppress
such reactions and prevent the concentration measurement being
affected, and to also make it easier to prevent heat from being
conducted to the first optical fiber and the second optical fiber,
it is also possible for the gas cell to be formed from quartz
glass, and for the light-emitting unit to be provided with a first
optical fiber via whose end surface measurement light is emitted, a
first lens that performs collimation on the measurement light
emitted from the end surface of the first optical fiber, and a
first holder that is made from resin and inside which are held the
first optical fiber and the first lens, and for the first aperture
and the first end surface to be formed in the first holder, and for
the light-receiving unit to be provided with a second optical fiber
via whose end surface measurement light is introduced, a second
lens that condenses measurement light onto the end surface of the
second optical fiber, and a second holder that is made from resin
and inside which are held the second optical fiber and the second
lens, and for the second aperture and the second end surface to be
formed in the second holder.
[0019] In order to ensure that the heater mechanism only heats the
gas cell, and that heat is prevented from being conducted directly
to the light-emitting unit and the light-receiving unit, it is also
possible for the heater mechanism to be a jacket heater that is
wrapped around the periphery of the gas cell, and is provided so as
to be separated from the first end surface and the second end
surface.
[0020] In order to enable the light-emitting unit and the
light-receiving unit to be arranged symmetrically to each other
centering on the gas cell, and to be placed naturally in positions
that correspond with the design values so as to prevent
discrepancies from being generated in the optical system, it is
also possible for there to be further provided a fixing mechanism
that fixes the first end surface of the light-emitting unit and the
second end surface of the light-receiving unit such that these are
a predetermined distance apart from each other, and a temporary
holding mechanism that temporarily holds the gas cell such that the
gas cell is able to slide in the direction of the optical axis of
the measurement light, and for a structure to be employed in which
the gas cell is gripped between the light-emitting unit and the
light-receiving unit by being pressed by repulsive force from the
first sealing component and the second sealing component.
[0021] An example of a specific structure in which the gas
concentration measurement apparatus according to the present
invention is favorably used is a structure in which the sample gas
introduced into the gas cell contains H.sub.2O.sub.2, and the
measurement light contains light in a near infrared region, and
there is further provided a concentration calculator that
calculates the concentration of the H.sub.2O.sub.2 introduced into
the gas cell interior based on the absorbance of the measurement
light received by the light-receiving unit.
[0022] Namely, the gas concentration measurement apparatus
according to the present invention includes a gas cell equipped
with a cell main body into whose interior sample gas is introduced,
an incident portion through which measurement light is irradiated
into an interior of the cell main body, and an emission portion
through which the measurement light that has passed through the
cell main body is emitted to the outside, and the gas concentration
measurement apparatus also includes a heater mechanism that heats
the gas cell, or the sample gas introduced into the gas cell, a
first optical fiber that is provided so as to emit measurement
light from an end surface thereof, and cause this measurement light
to be irradiated into the incident portion, and a second optical
fiber that is provided such that the measurement light that has
passed through the emission portion is irradiated onto an end
surface of the second optical fiber. In this case, the incident
portion and the emission portion have a double-glazed window
structure whose interior is either maintained in a vacuum, or holds
a gas.
[0023] If this type of structure is employed, then because the
incident portion and the emission portion have a double-glazed
window structure, even if heating is performed by the heater
mechanism in order to prevent the sample gas from becoming
reliquefied, it becomes difficult for this heat to be conducted to
the first optical fiber and the second optical fiber due to the
thermal insulation effect provided by the double-glazed window
structure. Accordingly, it is also difficult for temperature
changes to occur in the first optical fiber and the second optical
fiber, and the light-guiding characteristics thereof can be kept
substantially constant.
[0024] Furthermore, because it is possible to prevent the first
optical fiber and the second optical fiber from being affected by
heat simply by providing the double-glazed window structures of the
incident portion and the emission portion, the heater mechanism can
be provided directly in the gas cell without a two-fold structure,
in which an inner side wall and an outer side wall are provided in
the cell main body, having to be formed in order to prevent heat
from the cell main body being transmitted to the outside.
Accordingly, a sample gas circulating inside the gas cell can be
heated efficiently and reliquefaction can be reliably
prevented.
[0025] Because of these advantages, it is possible to maintain a
high level of accuracy when measuring gas concentrations while
using only a simple structure and without causing any excessive
energy consumption.
[0026] In order to make it easy for the optical path of measurement
light inside a gas cell to remain essentially the same as in a
conventional gas cell that does not have a double-glazed window
structure, and to make it possible to improve the accuracy of gas
concentration measurement, it is also possible for the
double-glazed window structure to include an inner window plate
that is attached to the cell main body, an outer window plate that
is provided at a predetermined distance from the inner window plate
so as to be parallel with the inner window plate, and an enclosing
wall that connects the inner window plate to the outer window plate
so as to form a closed space, and for an interior of the closed
space to be either maintained in a vacuum, or to hold a gas.
[0027] In order to improve assemblability and make it easy to form
an optical path from the first optical fiber to the second optical
fiber even if discrepancies are generated in the overall
configuration as a result of double-glazed window structures being
formed in the incident portion and the emission portion, and to
ensure that the fixing process does not place a heavy load on the
gas cell itself so that the lifespan of the product can be
extended, it is also possible to provide the cell main body with an
elongated shape, and to join the incident portion and the emission
portion respectively to a mutually different end portion of the
cell main body, and to further provide a supporting mechanism that
supports one point of a central portion of the cell main body.
[0028] In order to make it easy to attach the heater mechanism
uniformly to the interior of the cell main body so as to make it
possible to uniformly heat the sample gas inside the cell main
body, it is also possible to provide the cell main body with an
elongated shape, and to join the incident portion and the emission
portion respectively to a mutually different end portion of the
cell main body, and to further provide supporting mechanisms that
support both ends of the gas cell at the incident portion and the
emission portion. If this type of structure is employed, then the
gas cell can be stably supported, and the heater mechanism can be
provided in the cell main body, and it is possible to avoid a
situation in which components that might obstruct the interior
temperature of the cell being more uniformly and stably increased
are installed.
[0029] Furthermore, in order to make it easier for a sample gas to
be provided evenly throughout the cell main body, and to make it
more difficult for an uneven temperature distribution to occur in
the sample gas circulating through the gas cell interior, it is
also possible for the heater mechanism to be a jacket heater that
is wrapped around the cell main body.
[0030] In order to ensure that an equivalent mechanical strength
and an equivalent dimensional tolerance in the gas cell, as well as
equivalent light transmission characteristics for measurement light
as those that can be obtained conventionally can still be easily
achieved even if a double-glazed window structure is formed, it is
also possible for the gas cell to be formed from a plurality of
quartz glass pieces, and for the incident portion and the emission
portion to be bonded via optical contact bonding to the cell main
body. Moreover, if this type of structure is employed, then even if
the sample gas is one having a high degree of reactivity to metal,
it is still possible to prevent any changes from occurring in the
sample gas.
[0031] In order to make it difficult for problems to occur such as,
for example, the optical characteristics being changed due to air
from the surrounding environment that has been warmed by the heater
mechanism subsequently cooling and forming condensation on the
first optical fiber and the second optical fiber or on optical
components adjacent thereto, it is also possible for there to be
further provided a light-emitting unit that causes measurement
light that has been emitted from an end surface of the first
optical fiber provided inside the light-emitting unit to be emitted
into the gas cell via an emission aperture, a light-receiving unit
that causes measurement light that has passed through the gas cell
and is to be irradiated into an incident aperture to be irradiated
onto an end surface of a second optical fiber provided inside the
light-receiving unit, a first sealing component that is provided
between an incident surface, which is a surface on the incident
portion that measurement light first strikes from an outer side,
and a first end surface that is formed at a periphery of the
emission aperture of the light-emitting unit, so as to enclose the
periphery of the emission aperture, and a second sealing component
that is provided between an emission surface, which is a surface on
the emission portion that measurement light is ultimately emitted
from, and a second end surface that is formed at a periphery of the
incident aperture of the light-receiving unit, so as to enclose the
periphery of the incident aperture.
[0032] In order to ensure that the heater mechanism only heats the
gas cell, and that heat is prevented from being conducted directly
to the light-emitting unit and the light-receiving unit, it is also
possible for the heater mechanism to be a jacket heater that is
wrapped around the periphery of the gas cell, and is provided so as
to be separated from the first end surface and the second end
surface.
[0033] An example of a specific structure in which the gas
concentration measurement apparatus according to the present
invention is favorably used is a structure in which the gas
introduced into the gas cell contains H.sub.2O.sub.2, and the
measurement light contains light in a near infrared region, and
there is further provided a concentration calculator that
calculates the concentration of the H.sub.2O.sub.2 introduced into
the gas cell interior based on the absorbance of the measurement
light received by the light-receiving unit.
Effects of the Invention
[0034] In this way, according to the gas concentration measurement
apparatus according to the present invention, even if the gas cell
is being heated, there is substantially no conduction of this heat
to the respective optical fibers, and an environment in which it is
difficult for changes to occur in the light-guiding characteristics
of these optical fibers can be created. Moreover, because the first
sealing component and the second sealing component prevent air from
the surrounding environment from penetrating the peripheries of the
incident aperture and the emission aperture, it is possible to
prevent the effects of light absorption from gases other than the
sample gas, as well as the condensation of air from the surrounding
environment from reducing the accuracy of a gas concentration
measurement. Moreover, even if the components formed, for example,
from resin and the like that make up the gas concentration
measurement apparatus are partially vaporized by heat emitted by
the heater mechanism, this vaporized gas can be prevented from
penetrating the emission aperture and the incident aperture.
[0035] Moreover, according to the gas concentration measurement
apparatus according to the present invention, even if the gas cell
is being heated, the double-glazed window structure makes it
possible to ensure that there is substantially no conduction of
this heat to the respective optical fibers, and an environment in
which it is difficult for changes to occur in the light-guiding
characteristics can be created. Furthermore, it is possible to
ensure that the sample gas is directly heated by the heater
mechanism in the cell main body, and reliquefaction of the sample
gas within the cell main body can be reliably prevented.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIG. 1 is a typical view showing a gas concentration
measurement apparatus and a gas concentration control system
according to a first embodiment of the present invention.
[0037] FIG. 2 is a typical view showing the structure of the gas
concentration measurement apparatus according to the first
embodiment.
[0038] FIG. 3 is a typical perspective view showing the structures
of a gas cell according to the first embodiment and of instruments
adjacent thereto.
[0039] FIG. 4 is a typical front view showing the structures of the
gas cell according to the first embodiment and of instruments
adjacent thereto.
[0040] FIG. 5 is a typical cross-sectional view showing an internal
structure of a light-emitting unit according to the first
embodiment, and a positional relationship thereof relative to the
gas cell.
[0041] FIG. 6 is a typical cross-sectional view showing an internal
structure of a light-receiving unit according to the first
embodiment, and a positional relationship thereof relative to the
gas cell.
[0042] FIG. 7 is a typical perspective view showing the structures
of a gas cell according to a second embodiment of the present
invention and of instruments adjacent thereto.
[0043] FIG. 8 is a typical front view showing the structures of the
gas cell according to the second embodiment and of instruments
adjacent thereto.
[0044] FIG. 9 is a typical cross-sectional view showing a structure
in the vicinity of an incident side of a gas cell according to the
second embodiment.
[0045] FIG. 10 is a typical cross-sectional view showing a
structure in the vicinity of an emission side of a gas cell
according to the second embodiment.
[0046] FIG. 11 is a typical front view showing a variant example of
the gas cell according to the second embodiment.
BEST EMBODIMENTS FOR IMPLEMENTING THE INVENTION
[0047] A gas concentration measurement apparatus 100 and a gas
concentration control system 200 that employs this gas
concentration measurement apparatus 100 according to a first
embodiment of the present invention will now be described with
reference made to FIG. 1 through FIG. 6.
[0048] The gas concentration control system 200 shown in FIG. 1
supplies H.sub.2O.sub.2, which is a material gas in, for example, a
semiconductor manufacturing process, to an interior of a chamber
that is used to form an oxide film on a substrate while maintaining
this H.sub.2O.sub.2 at a constant concentration.
[0049] The gas concentration control system 200 generates
H.sub.2O.sub.2 gas and is formed by a vaporization apparatus VA
that controls the concentration of this H.sub.2O.sub.2 gas, and the
gas concentration measurement apparatus 100 that is provided
between the vaporization apparatus VA and a chamber and measures
the concentration of the H.sub.2O.sub.2 gas passing therethrough.
Note that if the H.sub.2O.sub.2 gas comes into contact with metal,
then decomposition is generated in the H.sub.2O.sub.2 gas, which
then forms H.sub.2O and O.sub.2. To prevent this, all of the
gas-contacting portions of the gas concentration control system 200
are formed using a material other than metal.
[0050] As is shown in FIG. 1, the vaporization apparatus VA is
provided with a carrier gas line CL on which is provided a mass
flow controller MFC that controls the flow rate of N.sub.2, which
is a carrier gas, a material liquid line ML on which are provided a
tank TN that internally contains an H.sub.2O.sub.2 solution and a
liquid mass flow meter LMFM that measures the flow rate of the
flowing H.sub.2O.sub.2 solution, and a vaporizer VP that is
provided at a junction point of the carrier gas line CL and the
material liquid line ML, and vaporizes the H.sub.2O.sub.2 solution
by heating it. Note that the H.sub.2O.sub.2 solution is
pressure-fed to the vaporizer VP by supplying N.sub.2 gas at a
predetermined pressure to an interior of the tank TN. Moreover, the
mass flow controller MFC controls the flow rate of the carrier gas
such that any discrepancy between the measured concentration of the
H.sub.2O.sub.2 gas, as measured by the gas concentration
measurement apparatus 100, and a target concentration is
minimized.
[0051] As is shown in FIG. 1, the gas concentration measurement
apparatus 100 is formed by a gas cell mechanism GS that is formed
such that H.sub.2O.sub.2 gas, which is a sample gas, circulates
through it and causes measurement light to be transmitted through
this H.sub.2O.sub.2 gas, and a gas concentration monitor GM that
causes measurement light to be generated and measures an absorbance
of the measurement light that has been transmitted through the
H.sub.2O.sub.2 gas in the gas cell mechanism GS.
[0052] More specifically, as is shown in FIG. 2, the gas
concentration measurement apparatus 100 measures the concentration
of H.sub.2O.sub.2 gas based on an NIR method, and is provided with
a reference light line L1 along which light whose wavelength is in
a near infrared region and that has been emitted from a halogen
light source HL is irradiated without passing through the gas cell
mechanism GS onto a detector DT as reference light, and a
measurement light line L2 along which light emitted from the
halogen light source HL travels via the gas cell mechanism GS to
the detector DT as measurement light. Moreover, this gas
concentration measurement apparatus 100 is also provided with two
switching mirrors, namely, a first switching mirror FM1 and a
second switching mirror FM2 that are used to switch an optical path
of the light emitted from the halogen light source HL to either the
reference light line L1 or the measurement light line L2. Namely,
when the light emitted from the halogen light source HL is to be
made to arrive at the detector DT via the reference light line L1,
the first switching mirror FM1 is removed from the optical path,
and the second switching mirror FM2 is placed on the optical path.
When the light emitted from the halogen light source HL is to be
made to arrive at the detector DT via the measurement light line
L2, the second switching mirror FM2 is removed from the optical
path, and the first switching mirror FM1 is placed on the optical
path.
[0053] In the detector DT, the absorbances in the absorption
wavelength regions of H202 and H.sub.2O are measured, for example,
from the intensities of the reference light and the measurement
light. The gas concentration monitor GM is further provided with a
gas concentration calculator C that calculates the concentrations
of the H.sub.2O.sub.2 gas and the H.sub.2O gas based on the
measured absorbances. The functions of the gas concentration
calculator C are achieved as a result of a program stored in the
memory of a computer, which is provided with a CPU, memory,
input/output means, and an AC/DC converter and the like, being
executed, and by each device working in mutual collaboration.
Namely, the gas concentration calculator C is formed so as to
calculate a gas concentration based on the absorbance and on a
calibration curve showing a relationship between the absorbance and
the gas concentration. The calibration curve is created in advance
based on experiments and the like.
[0054] Next, the gas cell mechanism GS will be described in detail
while referring to FIG. 3 through FIG. 6.
[0055] As is shown in FIG. 3 and FIG. 4, the gas cell mechanism GS
forms a portion of a line that connects the vaporizer VP to the
chamber, and is provided with a gas cell 1 into which
H.sub.2O.sub.2 gas is introduced, a light-emitting unit 2 that
causes measurement light to be irradiated into the gas cell 1, a
light-receiving unit 3 that receives measurement light that has
passed through the gas cell 1, and a fixing mechanism 4 that fixes
the gas cell 1, the light-emitting unit 2, and the light-receiving
unit 3 such that a predetermined positional relationship is
maintained between these components. Optically speaking, the
light-emitting unit 2 and the light-receiving unit 3 have the same
component elements and, as is shown in a front view in FIG. 4, the
gas cell mechanism GS can be disposed facing in either direction
with the gas cell 1 located in the center. Moreover, in the present
embodiment, the gas cell 1, the light-emitting unit 2, and the
light-receiving unit 3 are each formed as mutually independent
bodies.
[0056] The gas cell 1 is provided with a main body tube 11 having a
circular cylinder-shaped configuration that is disposed between the
light-emitting unit 2 and the light-receiving unit 3, a gas intake
tube 12 that is provided extending perpendicularly from an upstream
side of a side surface of the main body tube 11, and a gas
discharge tube 13 that is provided on a downstream side of the side
surface of the main body tube 11. The gas cell 1 is formed from
quartz glass and does not cause any significant decomposition
reaction in the H.sub.2O.sub.2 gas. An end surface on the upstream
side of the main body tube 11 is formed as an incident surface 14
into which measurement light emitted from the light-emitting unit 2
is irradiated, while an end surface on the downstream side thereof
is formed as an emission surface 15 from which measurement light
that has passed through the H202 gas is emitted to the outside.
Namely, the optical axis of the measurement light coincides with
the axis of the main body tube 11.
[0057] As is shown in FIG. 1, in order to prevent vaporized
H.sub.2O.sub.2 gas from cooling and becoming reliquefied, a jacket
heater JH, which is a heater mechanism, is wrapped around the gas
cell 1 so as to cover the periphery of the main body tube 11, and
the peripheries of the gas intake tube 12 and the gas discharge
tube 13. The jacket heater JH is provided with heating wires that
are embedded in a belt-shaped resin material, which functions as an
insulation material, and is wrapped such that it covers all side
surfaces of each of the tubes. Note that the jacket heater JH is
not in contact with the light-emitting unit 2 and the
light-receiving unit 3, but is provided at a distance
therefrom.
[0058] As is shown in FIG. 3, FIG. 4, and FIG. 5, the
light-emitting unit 2 is provided with a first optical fiber 21
that guides measurement light emitted from the halogen light source
HL, a first lens 22 that is provided so as to face an end surface
of the first optical fiber 21, and a first holder 23 that is formed
in a circular cylinder shape having substantially the same diameter
as the main body tube 11, with the first optical fiber 21 and first
lens 22 being held in an interior of the first holder 23.
[0059] The first holder 23 is made from resin, and an insertion
hole that is used to insert the first optical fiber 21 inside the
first holder 23 is opened in one end surface thereof, while an
emission aperture 24 through which measurement light that has
passed through the first lens 22 is emitted to the outside is
formed adjacent to the light emission side of the first lens 22 in
a first end surface 25, which is another end surface of the first
holder 23. A first recessed groove 26 is formed in a circular shape
centering on the emission aperture 24 in this first end surface 25.
The first end surface 25 is provided in close proximity to and
facing the incident surface 14 of the gas cell 1.
[0060] As is shown in FIG. 5, a first sealing component 5 in the
form of an O-ring that is seated inside the first recessed groove
26 is provided between the first end surface 25 of the
light-emitting unit 2 and the incident surface 14 of the gas cell
1. Namely, the first sealing component 5 is provided such that it
encloses the periphery of the emission aperture 24 with an airtight
seal. Moreover, when the light-emitting unit 2 and the gas cell 1
are fixed to the fixing mechanism 4, and the first sealing
component 5 has been compressed in the thickness direction thereof,
a first gap 7 is formed between the first end surface 25 and the
incident surface 14. In other words, in an assembled state, the
light-emitting unit 2 is not in direct contact with the gas cell 1,
and heat from the gas cell 1 can only be conducted thereto
indirectly via the first sealing component 5.
[0061] As is shown in FIG. 3, FIG. 4, and FIG. 6, the
light-receiving unit 3 is provided with a second lens 32 that
condenses the measurement light that has been transmitted through
the gas cell 1, a second optical fiber 31 that is provided such
that an end surface thereof faces the second lens 32 and guides
measurement light that has passed through the second lens 32 to the
detector DT, and a second holder 33 that is formed in a circular
cylinder shape having substantially the same diameter as the main
body tube 11, with the second lens 32 and second optical fiber 31
being held in an interior of the second holder 33.
[0062] The second holder 33 is made from resin, and an incident
aperture 34 through which measurement light that has passed through
the gas cell 1 is irradiated into the interior of the second holder
33 is formed adjacent to the light incident side of the second lens
32 in a second end surface 35, which is one end surface of the
second holder 33, while an insertion hole that is used to insert
the second optical fiber 31 inside the second holder 33 is opened
in another end surface thereof. A second recessed groove 36 is
formed in a circular shape centering on the incident aperture 34 in
this second end surface 35. The second end surface 35 is provided
in close proximity to and facing the emission surface 15 of the gas
cell 1.
[0063] As is shown in FIG. 6, a second sealing component 6 in the
form of an O-ring that is seated inside the second recessed groove
36 is provided between the emission surface 15 of the gas cell 1
and the second surface of the light-receiving unit 3. Namely, the
second sealing component 6 is provided such that it encloses the
periphery of the incident aperture 34 with an airtight seal.
Moreover, when the gas cell 1 and the light-receiving unit 3 are
fixed to the fixing mechanism 4, and the second sealing component 6
has been compressed in the thickness direction thereof, a second
gap 8 is formed between the emission surface 15 and the second end
surface 35. In other words, in an assembled state, the
light-receiving unit 3 is not in direct contact with the gas cell
1, and heat from the gas cell 1 can only be conducted thereto
indirectly via the second sealing component 6. Moreover, the first
gap 7 and the second gap 8 are formed having substantially the same
size, and the thickness dimensions of the first sealing component 5
and the second sealing component 6 prior to their deformation are
larger than the first gap 7 and the second gap 8.
[0064] The fixing mechanism 4 is provided with a metal base 41
having an elongated plate-shaped configuration, and a first
supporting pedestal 42, a second supporting pedestal 43, and a
central supporting pedestal 44 that are made from resin and are
provided standing upright on the base 41.
[0065] The first supporting pedestal 42 is a plate-shaped member
that is provided standing upright from one end side of the base 41,
and the light-emitting unit 2 is fixed thereto. More specifically,
as is shown in FIG. 5, the first end surface 25 side of the first
holder 23 is formed in a stepped circular cylinder shape, and a
small diameter portion thereof, which is on the first end surface
25 side, is inserted into the first supporting pedestal 42. An end
surface of the large diameter portion of the first holder 23 forms
a reference surface, and a structure is employed in which, when
this reference surface is abutted against one surface of the first
supporting pedestal 42, the first end surface 25 and another
surface of the first supporting pedestal 42 are substantially flush
with each other. In this state, the light-emitting unit 2 is fixed
in place by an anchoring screw on a side surface-side of the first
holder 23, so that the position of the first end surface 25 is
anchored.
[0066] The second supporting pedestal 43 is a plate-shaped member
that is provided standing upright from another end side of the base
41, and the light-receiving unit 3 is fixed thereto. More
specifically, as is shown in FIG. 6, the second end surface 35 side
of the second holder 33 is formed in a stepped circular cylinder
shape, and a small diameter portion thereof, which is on the second
end surface 35 side, is inserted into the second supporting
pedestal 43. An end surface of the large diameter portion of the
second holder 33 forms a reference surface, and a structure is
employed in which, when this reference surface is abutted against
another surface of the second supporting pedestal 43, the second
end surface 35 and one surface of the second supporting pedestal 43
are substantially flush with each other. In this state, the
light-receiving unit 3 is fixed in place by an anchoring screw on a
side surface-side of the second holder 33, so that the position of
the second end surface 35 is anchored.
[0067] In this manner, simply as a result of the first holder 23
and the second holder 33 being fixed to the fixing mechanism 4, the
first end surface 25 and the second end surface 35 can be
accurately placed a predetermined distance apart from each other.
Accordingly, the first optical fiber 21, the first lens 22, the
second lens 32, and the second optical fiber 31 can also be placed
in their proper positions on the optical axis in accordance with
the design.
[0068] The central supporting pedestal 44 is a temporary holding
mechanism on which the main body tube 11 of the gas cell 1 is
temporarily held such that the main body tube 11 is able to slide
in the direction of the optical axis of the measurement light. For
example, when the first holder 23 is fixed to the fixing mechanism
4, the gas cell 1 is inserted through the central supporting
pedestal 44, and the gas cell 1 is then pressed toward the first
supporting pedestal 42 side while the first sealing component 5 is
sandwiched between the first end surface 25 and the incident
surface 14. Next, while the second sealing component 6 is
sandwiched between the emission surface 15 and the second end
surface 35, the gas cell 1 is pressed towards the first supporting
pedestal 42 side as a result of the second holder 33 being fixed to
the second supporting pedestal 43. By mounting the gas cell 1 in
this manner, the gas cell 1 receives repulsive force from both the
first sealing component 5 and the second sealing component 6 in
their mutually opposite directions. As a result, the gas cell 1 is
moved to a position where the respective forces are balanced
relative to each other. Accordingly, the gas cell 1 moves naturally
until it is disposed in the center between the first end surface 25
and the second end surface 35 and, in this state, the gas cell 1 is
fixed by a screw relative to the central supporting pedestal 44.
Namely, using the fixing mechanism 4 and the temporary holding
mechanism, irrespective of the fact that the gas cell 1, the
light-emitting unit 2, and the light-receiving unit 3 are all
formed from mutually independent bodies, the gas cell 1 is held
between the light-emitting unit 2 and the light-receiving unit 3 by
pressure from the repulsive force from the first sealing component
5 and the second sealing component 6, and the optical components
belonging to each unit can be precisely placed in their proper
positions in accordance with the design.
[0069] According to the gas concentration measurement apparatus 100
having the above-described structure, because the first sealing
component 5 and the second sealing component 6 are provided such
that they enclose the emission aperture 24 and the incident
aperture 34 respectively with an airtight seal, it is possible to
prevent air from the environment surrounding the gas cell mechanism
GS from penetrating the emission aperture 24 and the incident
aperture 34. Moreover, even if a portion of the resin forming the
insulation material is vaporized by heat emitted by the jacket
heater JH, this vaporized gas can be prevented from penetrating the
emission aperture 24 and the incident aperture 34.
[0070] Accordingly, it is possible to prevent constituents other
than H.sub.2O.sub.2, which is a sample gas, from penetrating the
optical path of the measurement light, and prevent air from the
surrounding environment or gas from forming condensation on the
first lens 22 or the second lens 32 so as to cause the measured
light absorbance to change and thereby make it impossible to
accurately measure the gas concentration.
[0071] Moreover, because the light-emitting unit 2 and the
light-receiving unit 3 are not in direct contact with the gas cell
1, which is heated by the jacket heater, but only are only in
contact with the gas cell 1 indirectly via the resin O-rings, it is
possible to prevent the first optical fiber 21 and the second
optical fiber 31 being heated by thermal conduction from the gas
cell 1, and consequently causing a temperature change to occur.
Accordingly, it is possible to keep the light-guiding
characteristics of the optical fibers constant, and maintain a high
level of measurement accuracy when measuring a gas
concentration.
[0072] A variant example of the first embodiment will now be
described.
[0073] In the above-described first embodiment, the gas
concentration measurement apparatus of the present invention is
used to measure the concentration of H.sub.2O.sub.2 gas, however,
it is also possible to use this gas concentration measurement
apparatus to measure the concentrations of other types of gases.
For example, this gas concentration measurement apparatus may also
be used to measure gas concentrations when creating a gas for
medical applications, in order to obtain gas having a desired
concentration. In the case of a gas that does not react with metal,
which is not the case with H.sub.2O.sub.2 gas, the gas cell may be
formed from a material other than quartz glass. Moreover, the
light-emitting unit and the light-receiving unit may also be formed
from a material other than resin.
[0074] The first sealing component and the second sealing component
are not limited to being O-rings, and may also be formed from
caulking material that is provided so as to fill the gaps between,
for example, the gas cell and the light-emitting unit or the
light-receiving unit. Moreover, resin may be used to form the
O-rings, or alternatively, metal may be used. In addition, the
heater mechanism is not limited to being a jacket heater, and some
other heater mechanism may be used provided that it is able to heat
the gas cell, does not cause a sample gas circulating inside it to
decompose, and can be heated to a desired level without this
heating causing it to reliquefy.
[0075] A gas concentration measurement apparatus 100 and a gas
concentration control system 200 that employs this gas
concentration measurement apparatus 100 according to a second
embodiment of the present invention will now be described with
reference made to FIG. 7 through FIG. 10. Note that the structure
of the gas concentration measurement apparatus 100 according to the
second embodiment differs from that of the first embodiment, while
the structure of the gas concentration control system 200 is the
same as that shown in FIG. 1 and FIG. 2.
[0076] Next, the gas cell mechanism GS will be described in detail
with reference made to FIG. 7 through FIG. 10.
[0077] As is shown in FIG. 7 and FIG. 8, the gas cell mechanism GS
forms a portion of a line that connects the vaporizer VP to the
chamber, and is provided with a gas cell 1 into which
H.sub.2O.sub.2 gas is introduced, a light-emitting unit 2 that
causes measurement light to be irradiated into the gas cell 1, a
light-receiving unit 3 that receives measurement light that has
passed through the gas cell 1, and a fixing mechanism 4 that fixes
the gas cell 1, the light-emitting unit 2, and the light-receiving
unit 3 such that a predetermined positional relationship is
maintained between these components. Optically speaking, the
light-emitting unit 2 and the light-receiving unit 3 have the same
component elements and, as is shown in a front view in FIG. 8, the
gas cell mechanism GS can be disposed facing in either direction
with the gas cell 1 located in the center. Moreover, in the present
embodiment, the gas cell 1, the light-emitting unit 2, and the
light-receiving unit 3 are each formed as mutually independent
bodies.
[0078] The gas cell 1 is provided with a cell main body 1A into the
interior of which the sample gas is introduced, an incident portion
1B through which measurement light is irradiated into the interior
of the cell main body 1A, and an emission portion 1C through which
measurement light that has passed through the cell main body 1A is
emitted to the outside. The gas cell 11 is formed by a plurality of
quartz glass pieces and this makes it difficult for a decomposition
reaction to occur in the H.sub.2O.sub.2 gas. Moreover, the gas cell
1 is supported by the fixing mechanism 4 (described below) at both
ends thereof at the portions where the incident portion 1B and the
emission portion 1C are located.
[0079] The cell main body 1A is provided with a main body tube 11
having a circular cylinder-shaped configuration that is disposed
between the light-emitting unit 2 and the light-receiving unit 3, a
gas intake tube 12 that is provided extending perpendicularly from
an upstream side of a side surface of the main body tube 11, and a
gas discharge tube 13 that is provided on a downstream side of the
side surface of the main body tube 11.
[0080] The incident portion 1B and the emission portion 1C each
have a double-glazed window structure D whose interior is
maintained in a vacuum. In the present embodiment, a circular
cylinder-shaped tube having two closed ends that each have the same
diameter is bonded via an optical contact bond to the main body
tube 11 which has two open ends and has a circular cylinder-shaped
configuration.
[0081] Note that optical contact bonding refers to a method in
which pieces of smoothened glass can be bonded together simply by
being placed in contact with each other without any adhesive agent
being used, and refers to glass that is bonded, for example, at
room temperature or at high temperature. In an optical contact
bond, two pieces of glass are strongly bonded together by the Van
der Waals force between the two glass surfaces or by hydrogen
bonding between silanol groups that are formed by the absorption of
moisture from the air. Namely, in the gas cell 1, flat surfaces of
a plurality of quartz glass pieces can be placed in direct contact
with each other and bonded together without having to dissolve the
glass using an adhesive agent or chemical agent. Because of this,
no changes in the optical characteristics are brought about by the
adhesive agent or by the dissolution of the glass, while the vacuum
inside the double-glazed window structure D is maintained, and the
dimensional tolerance and strength of the gas cell 1 are kept the
same as those of the independent cell main body 1A by itself prior
to the bonding.
[0082] As is shown in FIG. 7 through FIG. 10, the incident portion
1B, the main body tube 11, and the emission portion 1C are provided
extending in a row in this sequence so as to form a single circular
cylinder-shaped tube in which the optical axis of the measurement
light is made to coincide with the axis of the main body tube 11.
Moreover, an end surface on the outer side of the incident portion
B is formed as the incident surface 14 into which measurement light
emitted from the light-emitting unit 2 is initially irradiated. In
contrast, an end surface on the outer side of the emission portion
1C, which is on the downstream side of the gas cell 1, is formed as
the emission surface 15 from which measurement light that has
passed through the H.sub.2O.sub.2 gas is finally transmitted.
[0083] As is shown in FIG. 9 and FIG. 10, the double-glazed window
structure D is provided with a circular plate-shaped inner window
plate D1 that is bonded via an optical contact bond to the cell
main body 1A, a circular plate-shaped outer window plate D2 that is
provided in parallel with and a predetermined distance away from
the inner window plate D1, and a circular cylinder-shaped enclosing
wall D3 whose two ends are both open, and that joins together the
inner window plate D1 and the outer window plate D2 such that a
closed space is formed inside the enclosing wall D3. Each of the
inner window plate D1, the outer window plate D2, and the enclosing
wall D3 are bonded together by optical contact.
[0084] As is shown in FIG. 1, in order to prevent vaporized
H.sub.2O.sub.2 gas from cooling and becoming reliquefied, a jacket
heater JH, which is a heater mechanism, is wrapped around the gas
cell 1 so as to cover the periphery of the main body tube 11, and
the peripheries of the gas intake tube 12 and the gas discharge
tube 13. The jacket heater JH is provided with heating wires that
are embedded in a belt-shaped resin material, which functions as an
insulation material, and is wrapped such that it covers all side
surfaces of each of the tubes. Note that, in the present
embodiment, because the gas cell 1 is supported at both ends
thereof at the portions where the incident portion 1B and the
emission portion 1C are located, but is not supported at the
portion of the cell main body 1A, which is wrapped with the jacket
heater JH, the jacket heater JH can be wrapped uniformly around the
main body tube 11 so that a uniform temperature distribution inside
the gas cell 1 can be achieved easily. More specifically, the
jacket heater JH is only provided at the portion where the main
body tube 11 is located, and the portions where the incident
portion 1B and the emission portion 1C are located are not covered.
Namely, the jacket heater JH is not in direct contact with the
light-emitting unit 2 and the light-receiving unit 3.
[0085] As is shown in FIG. 7, FIG. 8, and FIG. 9, the
light-emitting unit 2 is provided with the first optical fiber 21
that guides measurement light emitted from the halogen light source
HL, the first lens 22 that is provided so as to face an end surface
of the first optical fiber 21, and the first holder 23 that is
formed in a circular cylinder shape having substantially the same
diameter as the main body tube 11, with the first optical fiber 21
and first lens 22 being held in an interior of the first holder
23.
[0086] The first holder 23 is made from resin, and an insertion
hole that is used to insert the first optical fiber 21 inside the
first holder 23 is opened in the one end surface thereof, while an
emission aperture 24 through which measurement light that has
passed through the first lens 22 is emitted to the outside is
formed adjacent to the light emission side of the first lens 22 in
the first end surface 25, which is the other end surface of the
first holder 23. The first recessed groove 26 is formed in a
circular shape centering on the emission aperture 24 in this first
end surface 25. The first end surface 25 is provided in close
proximity to and facing the incident surface 14 of the gas cell
1.
[0087] As is shown in FIG. 9, the first sealing component 5, which
is in the form of an O-ring that is seated inside the first
recessed groove 26, is provided between the first end surface 25 of
the light-emitting unit 2 and the incident surface 14 of the gas
cell 1. Namely, the first sealing component 5 is provided such that
it encloses the periphery of the emission aperture 24 with an
airtight seal. Moreover, when the light-emitting unit 2 and the gas
cell 1 are fixed to the fixing mechanism 4, and the first sealing
component 5 has been compressed in the thickness direction thereof,
the first gap 7 is formed between the first end surface 25 and the
incident surface 14. In other words, in an assembled state, the
light-emitting unit 2 is not in direct contact with the gas cell
1.
[0088] As is shown in FIG. 7, FIG. 8, and FIG. 10, the
light-receiving unit 3 is provided with the second lens 32 that
condenses the measurement light that has been transmitted through
the gas cell 1, the second optical fiber 31 that is provided such
that an end surface thereof faces the second lens 32 and guides
measurement light that has passed through the second lens 32 to the
detector DT, and the second holder 33 that is formed in a circular
cylinder shape having substantially the same diameter as the main
body tube 11, with the second lens 32 and second optical fiber 31
being held in an interior of the second holder 33.
[0089] The second holder 33 is made from resin, and the incident
aperture 34 through which measurement light that has passed through
the gas cell 1 is irradiated into the interior of the second holder
33 is formed adjacent to the light incident side of the second lens
32 in the second end surface 35, which is the one end surface of
the second holder 33, while the insertion hole that is used to
insert the second optical fiber 31 inside the second holder 33 is
opened in the other end surface thereof. The second recessed groove
36 is formed in a circular shape centering on the incident aperture
34 in this second end surface 35. The second end surface 35 is
provided in close proximity to and facing the emission surface 15
of the gas cell 1.
[0090] As is shown in FIG. 10, the second sealing component 6,
which is in the form of an O-ring that is seated inside the second
recessed groove 36, is provided between the emission surface 15 of
the gas cell 1 and the second surface of the light-receiving unit
3. Namely, the second sealing component 6 is provided such that it
encloses the periphery of the incident aperture 34 with an airtight
seal. Moreover, when the gas cell 1 and the light-receiving unit 3
are fixed to the fixing mechanism 4, and the second sealing
component 6 has been compressed in the thickness direction thereof,
the second gap 8 is formed between the emission surface 15 and the
second surface 35. In other words, in an assembled state, the
light-receiving unit 3 is not in direct contact with the gas cell
1.
[0091] Moreover, the first gap 7 and the second gap 8 are formed
having substantially the same size, and the thickness dimensions of
the first sealing component 5 and the second sealing component 6
prior to their deformation are larger than the first gap 7 and the
second gap 8.
[0092] The fixing mechanism 4 is provided with the metal base 41
having an elongated plate-shaped configuration, and the first
supporting pedestal 42, the second supporting pedestal 43, an
incident portion supporting pedestal 44, and an emission portion
supporting pedestal 45 that are made from resin and are provided
standing upright on the base 41.
[0093] The first supporting pedestal 42 is a plate-shaped member
that is provided standing upright from the one end side of the base
41, and the light-emitting unit 2 is fixed thereto. More
specifically, as is shown in FIG. 9, the first end surface 25 side
of the first holder 23 is formed in a stepped circular cylinder
shape, and a small diameter portion thereof, which is on the first
end surface 25 side, is inserted into the first supporting pedestal
42. An end surface of the large diameter portion of the first
holder 23 forms a reference surface, and a structure is employed in
which, when this reference surface is abutted against the one
surface of the first supporting pedestal 42, the first end surface
25 and the other surface of the first supporting pedestal 42 are
substantially flush with each other. In this state, the
light-emitting unit 2 is fixed in place by an anchoring screw on a
side surface-side of the first holder 23, so that the position of
the first end surface 25 is anchored.
[0094] The second supporting pedestal 43 is a plate-shaped member
that is provided standing upright from the other end side of the
base 41, and the light-receiving unit 3 is fixed thereto. More
specifically, as is shown in FIG. 10, the second end surface 35
side of the second holder 33 is formed in a stepped circular
cylinder shape, and a small diameter portion thereof, which is on
the second end surface 35 side, is inserted into the second
supporting pedestal 43. An end surface of the large diameter
portion of the second holder 33 forms a reference surface, and a
structure is employed in which, when this reference surface is
abutted against the other surface of the second supporting pedestal
43, the second end surface 35 and the one surface of the second
supporting pedestal 43 are substantially flush with each other. In
this state, the light-receiving unit 3 is fixed in place by an
anchoring screw on a side surface-side of the second holder 33, so
that the position of the second end surface 35 is anchored.
[0095] In this manner, simply as a result of the first holder 23
and the second holder 33 being fixed to the fixing mechanism 4, the
first end surface 25 and the second end surface 35 can be
accurately placed a predetermined distance apart from each other.
Accordingly, the first optical fiber 21, the first lens 22, the
second lens 32, and the second optical fiber 31 can also be placed
in their proper positions on the optical axis in accordance with
the design.
[0096] The incident portion supporting pedestal 44 and the emission
portion supporting pedestal 45 are formed such that they are only
in contact with the portions of the gas cell 1 where the
double-glazed window structure D is formed. Namely, in the gas cell
1, the incident portion supporting pedestal 44 and the emission
portion supporting pedestal 45 are in contact with the outer side
circumferential surface of the enclosing wall D3 in the portions
that are most resistant to a thermal effect from the jacket heater
JH, which are also the portions where the temperature is most able
to remain constant. Note that it is also possible for a portion of
each of the incident portion supporting pedestal 44 and the
emission portion supporting pedestal 45 to protrude from the
incident portion 1B and the emission portion 1C in such a way that
they also support a portion of the cell main body 1A.
[0097] According to the gas concentration measurement apparatus 100
that is formed in the above-described manner, because the incident
portion 1B and the emission portion 1C, which are the both end
portions of the gas cell 1 on the upstream and downstream sides
thereof, have the double-glazed window structure D, heat from the
jacket heater JH is insulated by the incident portion 1B and the
emission portion 1C, and it is difficult for this heat to be
conducted to the light-emitting unit 2 and the light-receiving unit
3. Because of this, even if a sample gas is sufficiently heated
such that it does not become reliquefied inside the gas cell 1, it
is possible to prevent the light-guiding characteristics of the
respective optical fibers being changed by this heat, and causing a
concomitant change in the accuracy of the concentration
measurement.
[0098] Moreover, it is also difficult for the heat from the jacket
heater JH to be conducted directly to the incident portion
supporting pedestal 44 and the emission portion supporting pedestal
45, and the temperatures of each of these can easily be kept
constant. Accordingly, in spite of the fact that both ends of the
gas cell 1 are being supported, because it is difficult for thermal
deformation to be generated independently in both the incident
portion supporting pedestal 44 and the emission portion supporting
pedestal 45, the attitude of the gas cell 1 can be maintained
constantly at the same attitude. Because of this, even if heating
of the sample gas does take place, the optical axis of the
measurement light can be made to remain substantially the same as
the optical axis of the gas cell 1, and any change in the optical
characteristics thereof can be prevented. As a consequence, a high
degree of concentration measurement accuracy can be maintained.
Note that it is also possible for the first supporting pedestal 42
and the incident portion supporting pedestal 44, which are standing
upright on the base 41, to be formed as a single body, and for the
second supporting pedestal 43 and the emission portion supporting
pedestal 45, which are standing upright on the base 41, to also be
formed as a single body. Namely, a first engaging portion may be
provided that positions both the light-emitting unit 2 and the
incident portion 1B on one single base, and a second engaging
portion may be provided that positions both the light-receiving
unit 3 and the emission portion 1C on another single base. If this
type of structure is employed, then simply by mounting the gas cell
1, the light-emitting unit 2, and the light-receiving unit 3 on a
base, the optical axes of each can be made to coincide precisely,
and the complexity of this task can be alleviated.
[0099] Furthermore, because the first sealing component 5 and the
second sealing component 6 are provided so as to enclose the
emission aperture 24 and the incident aperture 34 respectively with
airtight seals, air from the environment surrounding the gas cell
mechanism GS can be prevented from penetrating the emission
aperture 24 and the incident aperture 34. Even if a portion of the
resin forming the insulation material does become vaporized by the
heat generated by the jacket heater JH, this vaporized gas can
still be prevented from penetrating the emission aperture 24 and
the incident aperture 34.
[0100] Accordingly, it is possible to prevent a measured absorbance
being changed because of elements other than H.sub.2O.sub.2, which
is a sample gas, penetrating the optical path of measured light, or
because of gas or air from the surrounding environment causing the
first lens 22 and the second lens 32 to become fogged, and thereby
preventing the gas concentration from being measured
accurately.
[0101] A variant example of the second embodiment will now be
described.
[0102] In the second embodiment a structure is employed in which
the gas cell 1 is supported at both ends thereof by the incident
portion 1B and the emission portion 1C being fixed by the incident
portion fixing pedestal 44 and the emission portion fixing pedestal
45 of the fixing mechanism 4. However, as is shown in FIG. 11, it
is also possible to provide a central portion supporting pedestal
46 that only provides support at one point, namely, in the central
portion of the cell main body 1A of the gas cell 1.
[0103] If this type of structure is employed, then even if
assembling errors or the like relative to the optical axis
direction occur in the gas cell 1 so that the configuration from
the incident portion 1B to the emission portion 1C differs from the
design values, compared with when support is provided at the two
ends, it is still easy to assemble the gas cell 1 in such a way
that light can be transmitted from the light-emitting unit 2 to the
light-receiving unit 3. Moreover, because the central portion of
the gas cell 1 is supported at a single point, it is more difficult
for a load to be generated by configuration errors than when
support is provided at both ends, and an increased lifespan can be
obtained from the finished product.
[0104] In the above-described second embodiment, the gas
concentration measurement apparatus of the present invention is
used to measure the concentration of H.sub.2O.sub.2 gas, however,
it may also be used to measure concentrations of other types of
gases. For example, this gas concentration measurement apparatus
may also be used to measure gas concentrations when creating a gas
for medical applications, in order to obtain gas having a desired
concentration. In the case of a gas that does not react with metal,
which is not the case with H.sub.2O.sub.2 gas, the gas cell may be
formed from a material other than quartz glass. Moreover, the
light-emitting unit and the light-receiving unit may also be formed
from a material other than resin.
[0105] Moreover, the degree of vacuum inside the closed space of
the double-glazed window structure may be set as is appropriate,
and it is only necessary for this degree of vacuum to provide
sufficient insulation to prevent any effects of the heat from the
heater mechanism from appearing in the respective optical fibers.
Moreover, it is also possible for the closed internal space inside
the double-glazed window structure to not be set in a vacuum, but
for this closed space to instead be filled with a gas. For example,
the interior of this closed space may also be filled with a
different type of gas from the sample gas, or with a gas having a
different absorption wavelength from the sample gas. Specific
examples include filling the closed space with gas in the form of
dried air from which water vapor has been removed, or else causing
this gas to circulate inside the closed space. If this type of
structure is employed, then the gas inside the closed space
functions as a translucent insulation material even if the closed
space is not a vacuum, and prevents heat from the heater mechanism
from being conveyed to the respective optical fibers. Furthermore,
if dry air is used, then even though a gas is present inside the
double-glazed window structure, there is no light absorption by
H.sub.2O, and it is possible to prevent this type of light
absorption from causing any reduction in accuracy when measuring
the concentration of, for example, H.sub.2O.sub.2 or another gas.
Moreover, the interior of the closed space is not limited to being
sealed completely airtight, and it is also possible for there to be
an extremely slight gap such as might eventuate, for example, as
the degree of vacuum deteriorates over time. Note that if a gas is
present inside the double-glazed window structure, then this gas
may be at the same pressure as the atmospheric pressure or may be
depressurized to below atmospheric pressure.
[0106] Furthermore, the diameter of the double-glazed window
structure may also be different from the diameter of the main body
tube. Furthermore, it is also possible for the light-emitting unit
and the light-receiving unit to be placed in direct contact
respectively with the incident portion and the emission portion
without a sealing component being interposed between them. In this
type of structure as well, no thermal conduction to the
light-emitting unit and the light-receiving unit is able to occur
because of the insulation functions of the incident portion and the
emission portion, and the temperature of the respective optical
fibers can be kept constant.
[0107] The heater mechanism is not limited to a type of heater
mechanism that directly heats the gas cell and it is also possible,
for example, to heat the sample gas in a tube before the sample gas
is introduced into the gas cell.
[0108] The first sealing component and the second sealing component
are not limited to being O-rings, and it is also possible, for
example for these sealing components to be in the form of caulking
that is provided such that it fills the gaps between the
light-emitting unit and the gas cell or the light-receiving unit
and the gas cell. In addition, any O-ring may be formed from resin,
or may be formed from metal. The heater mechanism is also not
limited to being a jacket heater, and any type of heater that heats
the gas cell, that does not decompose any sample gas internally
circulating inside itself, and that can be heated sufficiently
without becoming liquefied may be used.
[0109] Furthermore, it should be understood that the present
invention is not limited to the above-described embodiments, and
that various modifications and the like may be made thereto insofar
as they do not depart from the spirit or scope of the present
invention.
DESCRIPTION OF THE REFERENCE NUMERALS
[0110] 100 . . . Gas concentration measurement apparatus [0111] 1 .
. . Gas cell [0112] 14 . . . Incident surface [0113] 15 . . .
Emission surface [0114] 1A . . . Cell main body [0115] 1B . . .
Incident portion [0116] 1C . . . Emission portion [0117] 2 . . .
Light-emitting unit [0118] 21 . . . First optical fiber [0119] 22 .
. . First lens [0120] 23 . . . First holder [0121] 24 . . .
Emission aperture [0122] 25 . . . First end surface [0123] 3 . . .
Light-receiving unit [0124] 31 . . . Second optical fiber [0125] 32
. . . Second lens [0126] 33 . . . Second holder [0127] 34 . . .
Incident aperture [0128] 35 . . . Second end surface [0129] 4 . . .
Fixing mechanism [0130] 5 . . . First sealing component [0131] 6 .
. . Second sealing component
* * * * *